The primary objective of this proposal is to investigate the mechanisms of host defense that are important for recovery from acute viral infections of the CNS, using SIN encephalitis as a model system. This investigation will provide new insights into virus-host interactions and will thereby provide a biologic framework for the development of new therapeutic antiviral strategies. This proposal will focus on understanding the mechanisms by which MAbs to the SIN E2 envelope glycoprotein restrict SIN gene expression in neurons. Based on preliminary findings demonstrating that the E2 envelope glycoprotein upregulates gene expression in neuroblastoma cells and that anti-E2 MAbs that restrict SIN replication enter virally infected neurons, this research proposal will investigate two principal hypotheses: (1) E2 regulates SIN gene expression and anti-E2 MAbs inhibit SIN replication by altering this regulatory effect; and (2) anti-E2 MAbs act intracellulary to inhibit SIN replication. To investigate the first hypothesis, this proposal will analyze (1) the effects of mutations at amino acid position 55 on the regulation of SIN gene expression in neurons and nonneuronal cells; (2) the role of the transmembrane and cytoplasmic domains of E2 in the regulation of SIN gene expression; (3) the effects of anti-E2 MAbs on E2-mediated upregulation of SIN gene expression; and (4) the role of the cytoplasmic domain of E2 in anti-E2 MAb-mediated inhibition of SIN gene expression. To investigate the second hypothesis, recombinant SIN/immunoglobulin (Ig) gene chimeras will be engineered to express intracellular anti-E2 MAbs in different cellular compartments and the effects of expression of anti-E2 MAbs in different neuronal compartments on SIN replication will be determined.